Photonic Crystal Nanocavities With an Average Q Factor of 1.9 Million Fabricated on a 300-mm-Wide SOI Wafer Using a CMOS-Compatible Process

Electron-beam lithography allows precise photonic crystal (PC) fabrication, but is not suitable for mass production. Therefore, the development and optimization of CMOS-compatible processes is necessary to implement unique nanocavity technologies in optoelectronic circuits. We investigated the quality factors (Q) and the resonant wavelengths (λ) of PC heterostructure nanocavities fabricated by the 193-nm argon fluoride immersion lithography on a 300-mm-wide silicon-on-insulator wafer. We measured 30 cavities distributed over nine chips at various positions of the wafer. An average Q of 1.9 million was obtained for the 30 cavities, and the highest value was 2.5 million, which is the highest Q reported so far for a nanocavity fabricated by photolithography. Such high Q were realized by the improvements of the nanocavity design and the fabrication process. All nanocavities exhibited a Q of larger than 1 million and the fluctuation of the chip-averaged Q was independent of the chip location. On the other hand, the measured λ tended to shift to shorter wavelengths as the distance between the nanocavity and the substrate center increased. Among the nine chips, the difference of the chip-averaged λ was as large as 8.0 nm. We consider that a systematic shift of the average air-hole radius by several nanometers is responsible for the large fluctuation of the chip-averaged λ. These statistical studies provide important hints to accelerate the application study of PC high-Q nanocavities.